The opening Chapters summarise the previous work on electrical conductivity, density and ultra-violet spectroscopy in fused salt systems, and on the melting process for ionic substances. The aim of the present work is defined in relation to this previous knowledge. The electrical conductivities and densities of fused KNO3 - Ba(NO3)2 mixtures were measured. The conductivity of KNO3 is depressed when Ba(NO3)2 is added, so the divalent ions restrict ionic migration. Consistently with this interpretation, the equivalent volumes of the molten mixtures decreased with rising barium concentration, and the fraction of the volume actually occupied by the ions also decreased. These results contrast sharply with correspond-ing results for ionic crystals, which points to limitations in the applicability of the 'quasi-crystalline' model to ionic melts. The near ultra-violet absorption spectra of the alkali metal nitrates, silver, thallous and ammonium nitrates, nitric acid and iso-propyl nitrate were measured at temperatures up to and beyond their melting-points. The weak band at 33 kcm-1 is due to an internal transition (n -4.1r* ) in the nitrate ion; its maximum frequency, E(2), depends on the identity of the cation, on the temperature and on crystal structure. 7,(2) is determined largely by the first shell of cations around each nitrate ion; for a given salt an increase in E(2) corresponds to a decrease in the nearest cation - oxygen distance, and vice versa. This leads to the important conclusion that the nearest-neighbour cation - oxygen separation decreases on fusion, in spite of the macroscopic increase in volume. Similar conclusions were reached about the melting process in sodium and potassium nitrites. The temperature dependence of the % transmission of a thin film of salt at fixed frequency provided a means for determining transition temperatures and for studying hysteresis in phase transformations.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:602276 |
| Date | January 1963 |
| Creators | Cleaver, Brian |
| Publisher | Imperial College London |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/10044/1/13672 |
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